Frequency changer



May 23, 1950 E. 5. LINDER FREQUENCY CHANGER Filed Oct. 23, 1 945 INVENTOR www ATTORNEY ERNEST fi. UNDER Patented May 23, 1950 FREQUENCY CHANGER Ernest, G. Linder, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application October 23, 1945, Serial No. 623,947

18 Claims.

My invention relates to electron discharge devices and associated circuits, more particularly to such devices and circuits useful at ultra high frequencies and capable of frequency change.

The present application is directed to an improved device of the kind described and claimed in patent application Serial No. 385,447, filed March 27, 1941, now Patent No. 2,401,945, dated June 11, 1946, and assigned to the same assignee as the present application.

It is a principal object of my invention to provide an improved type electron discharge device and associated circuit useful at ultra high frequencies and employing cavity resonators, and more particularly to provide such a device and circuit useful as a frequency changer.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims, but the invention itself will best be understood by reference to the following description taken in connection with the accompanying drawing in which Figure 1 is a partially schematic longitudinal section of an electron discharge device and associated circuit made according to my invention, Figure 2 is a graph showing the principles of operation of m invention, and Figure 3 is a partially schematic longitudinal section of a modification of the device shown in Figure 1.

In a device made according to my invention an electron beam is modulated at a predetermined fundamental high frequency to provide equally spaced bunches of electrons. The bunches are then subjected to a high frequency field of a'lower frequency and having a predetermined voltage characteristic for successively and at increased voltage increments accelerating the bunches of electrons to compress the electron bunches into spaced groups of bunches within a field-free space. The spacing-between electron bunches in each group becomes decreased in this field-free space. The groups of compressed bunches are then utilized to excite an output resonator at a higher frequency than the fundamental frequency initially applied to the electron stream.

In Figure 1 is shown a device and circuit made according to my invention. It may include an evacuated elongated envelope I having at one end an indirectly heated cathode II and at the other a collector I2. Adjacent the cathode is a control electrode I3 for modulating the electron stream. Between the control electrode I3 and the collector I2 there is a hollow tubularly shaped electrode I4 having an aperture I6 adjacent the electrode I3 and a partition I5, the partitionand the end of the electrode I4 adjacent collector I2 being provided with apertures and reentrant portions I! and I8 to provide a gap past which the compressed groups of electrons are directed. In effect the portion of the electrode I4 adjacent the collector I2 provides a cavity resonator I9 having an output coupling loop I9. A magnetic coil 20 may be used for maintaining the beam of electrons focused.

A first high frequency oscillator 2I is connected between the cathode I I and the control electrode I3 for applying a voltage of one frequency ii to the electrode I3 to provide equally spaced electron bunches as indicated in the top portion Ip of the graph, Figure 2. .Biasing voltage source 23 biases the tube to cut-01f when no oscillator voltageis applied. A second oscillator 22 is connected between the cathode and the electrode I4 through an accelerating biasing voltage source 24. The frequency f2 of this second oscillator 22 and the voltage wave form is as indicated in the second line of the graph, Figure 2. In the particular case shown the frequency i2 is onequarter the frequency of the first oscillator. This second frequency can be varied so that the ratio of frequencies may .be any number, so longas the frequency of the oscillator 22 is less than that of the oscillator 2I. The result of applying this voltage E22 is to compress the electron bunches into groups as is shown in the lower part of the graph, Figure 2, so that in effect groups of electrons are produced with the spacing between the bunches in each group reduced. The time elements, voltages and spacings are so chosen that the bunches of each group of electrons have a transit time past the gap in the resonator I9 and a phase relationship necessary to excite this resonator at a higher frequency than that of oscillator 2|. The collector I2 is maintained at a positive potential with respect to the cathode by a voltage source 25. w 7 Y In more detail, electron bunches leave the electrode I3 spaced at even intervals as indicated by Ip. The accelerating voltage applied to the electrode I 4 is of saw-tooth shape and preferably parabolic since this is the type of voltage form necessary .to produce the results desired. For example, consider the case in which each bunch is given a velocity increment A1; in excess of the preceding bunches. The resulting velocities will be Un is equal to 221+ (n1)Av. It will thus be seen that as each bunch emerges into the space between electrode [3 and the aperture is it will receive a voltage increment such that each successive pulse is subjected to a successively increasing accelerating voltage, the last bunch crossing this space when the potential of electrode i4 is greatest receiving the greatest acceleration. Each of the bunches on entering the field-free space within the electrode 1 i retains the velocity it had on passing through the aperture "5 so that the bunches approach closer to each other as they reach the partition IS, the faster bunches overtaking the slower bunches and forming spaced groups of closely spaced bunches. The parameters are so chosen that the bunches of each group pass the gap between the portions l1 and 18 of resonator is in proper phase to continuously excite the resonator, the spacing between adjacent bunches being such that the resonator oscillates at its resonant frequency through at least one cycle before the next bunch arrives. The resonator I9 is so constructed that its resonant frequency is substantially cessive decelerating electrodes '30 which are .maintaine'd'at successively lower constant potentials by means of voltage source 32 and voltage divider 3i. Thisreverse field decelerates the slower bunches to a greater amount than the fasterbunches, thus increasing'the velocity difference ftherebetween, which. reduces the drift distance required for a given degree of compression of the bunches, that is, for a given output frequency. If desired a focusing electrode 34 may be positioned between resonator I 9 and the last decelerating. electrode 3!! at a voltage maintained. at the desired level by voltage source 35.

While I have indicated the preferred, embodiments'of my invention of which I am now aware and-have also. indicated only one specific application for which my invention may be employed, it will be apparent that my invention .is by no means limited to the exactform'sillustrated or the use indicated, but that many variations may be made in the particular structure used and the purposefor which it is employed without departing from thescope of my invention as set forth in the appended claims.

WhatI claim as new is: 7

-1 A- frequency changer including means for supplying a stream of electrons along a predetermined path, means for modulating said'electronstream at a predetermined frequency to produce equally-spaced bunches of electrons of substantially the same velocityalong said path, means for accelerating a plurality of successive bunches to increasingly greater velocities, means causing compression of saiddifferentially accel erated bunches into a group of closely-spaced bunches, and tuned means for extracting energy from said group of closely-spaced bunches at a substantially higher frequency than said predetermined frequency 2. A frequency chan er f cluding means for supplying a stream 'bf ele'ctrons along a predetermined path, means for modulating said electron stream at a predetermined frequency to produce equally-spaced bunches of electrons of substantially the same velocity along said path, means for subjecting a plurality of said bunches to an electric field of increasing strength for accelerating successive bunches at increasingly greater increments, means'providing a shielded space along said path for receiving said diiferentially accelerated bunches for causing compression of said bunches into a group of closelyspaced bunches, and tuned means for extracting energy from said group of closely-spaced bunches at a substantially higher frequency than said predetermined frequency.

3. A frequency changer including means for supplying a stream of electrons along a predetermined path, means for modulating said electron stream at a predetermined frequency to produce equally-spaced bunches of electrons of substantially the same velocity along said path,,periodic means for accelerating successive bunches of electrons'in each cycle of said periodic accelcrating means to successively higher velocities, means for compressing successive bunches of said differentially accelerated bunches in each cycle into a group of closely-spaced, bunches, and tuned means for extracting energy at ,a substantially higher frequency than said predetermined frequency from each group of closely-spaced bunches of electrons.

4. A frequency changer including means for supplying a stream of electrons along a predetermined path, means for modulating said electron stream at a predeterminedfrequency to produce equally-spaced bunches of electrons of substantially the same velocity along said path, means for subjecting said-bunches of-electrons to 'a periodic electric field of substantially lower frequency than said predetermined frequency and increasing in strength with time throughout the major portion of each cycle thereof for accelerating successive bunches in each cycle thereof to successively greater velocities, -means providing a shielded space along said path for receiving said differentially accelerated bunches for compressing said'bunches in each cycle into a group of closely-spaced bunches, and tuned means for extracting energy from each group of. closelyspaced bunches at a substantially higher frequency than said predetermined frequency, V

5. A frequency changer comprising means for supplying a stream of electrons along a predetermined path, means including a control electrode in said path for modulatingsaid electron stream ata predetermined frequency to produce equallys'pacedelectron bunches of substantially the same velocity along saidnpath, a second electrode in said path beyondsaid control electrode, a source of potential. of substantially lower frequency than said predetermined frequency and having a wave form which increases in amplitude with timeduring the major portion of each cycle thereof and connected to said second electrode for accelerating successive bunches in each cycle at increasingly greater increments, means providing a shielded space along said path for receiving said differentially accelerated bunches for causing said bunches in each oycle to form a group of closely spaced bunchesf and tuned means for extracting energy from said closely spaced bunchesyof each group at a higherfrequency than said predetermined frequency. i

" 6. A frequency changer according to claim 5.

wherein said source has a saw-tooth parabolic wave form of increasing amplitude with time.

7. A frequency changing system including means comprising a cathode for supplying a stream of electrons along a predetermined path, a control electrode adjacent said cathode, a source of potential of a predetermined high frequency connected to said control electrode for modulating said stream to produce equally-spaced bunches of electrons along said ath, a second electrode in the path of said equally-spaced bunches of electrons, a second source of potential having a frequency substantially less than said predetermined frequency and having a wave form of saw-tooth parabolic shape and connected to said second electrode for accelerating successive equally-spaced bunches in each cycle to increasingly higher velocities, a drift tube providing a shielded space along said path through which said differentially accelerated bunche of electrons are directed, whereby said bunches become compressed into groups of closely-spaced bunches in traversing said space, and tuned means for extracting energy from said closelyspaced bunches and including a cavity resonator disposed in said path, the fundamental frequency of said resonator being substantially higher than said predetermined frequency.

8. A frequency changer according to claim 7 wherein said drift tube comprises a tubular member having aligned apertures at its ends and including said output cavity resonator within said tubular member.

9. A frequency changer according to claim 8, wherein said tubular member has a partition therein intermediate its ends, said partition hav ing an aperture aligned with said end apertures and being more closely adjacent the end of said tubular member remote from said second electrode, said cavity resonator being formed by said partition and tubular member.

10. An electron discharge device having a cathode for supplying electrons along a predetermined path, means in said path for applying an electric field of one high frequency to said electrons to obtain equally spaced bunches of electrons of substantially the same velocity, a second means in said path for applying an accelerating electric field having a high frequency substantially less than said one frequency to said equally spaced bunches of electrons substantially for differentially accelerating successive bunches, means providing a shielded space through which said difierentially accelerated bunches of electrons are directed to compress said bunches in each cycle into a group of closely spaced bunches, means in said space for applying a decelerating field to said bunches of electrons, and tuned means for extracting energy from decelerated compressed groups of electrons at a frequency which is substantially higher than said one frequency.

11. An electron discharge device having a cathode for supplying electrons along a predetermined path, means for collecting said electrons, means including a control electrode adjacent said cathode in the path of said electrons for applying a modulating electric field of one high frequency to said electrons for providing equally spaced electron bunches, a second electrode positioned between said control electrode and said collector and comprising a tubular member having a partition intermediate the ends thereof, the ends of said tubular electrode and said partition having aligned apertures, said partition being more close- 1y adjacent the end of said tubular member adiacent said collector and providing a cavity resonator within said tubular member, the portion of said tubular member between the end thereof adjacent said control electrode and said partition providing a continuous drift space, and means for applying to said tubular member a modulating potential having a high frequency substantially less than said one frequency, whereby said bunches of electrons become compressed into groups of closely spaced bunches within said drift space prior to passage through said apertured partition.

12. An electron discharge device having a cathode for supplying electrons along a predetermined path, means including a control electrode adjacent said cathode in the path of said electrons for applying a modulating electric field of one high frequency to said electrons for providing equally spaced electron bunches, a second electrode positioned in the path of said bunches and comprising a tubular member extending along aid path and having aligned apertures at its ends and including a cavity resonator within said tubular member, the portion of said tubular member between the end thereof nearest the control electrode and said cavity resonator providing a continuous drift space, and means for applying to said second cathode a modulating potential having a high frequency less than said one frequency whereby said bunches of electrons become compressed into a group of closely spaced bunches within said drift space prior to passage through said resonator.

13. An electron discharge device having a cathode for supplying electrons along a predetermined path, means including a control electrode adjacent said cathode in the path of said electrons, for applying a modulating electric field of one high frequency to said electrons for providing equally spaced electron bunches, a second electrode positioned in the path of said bunches and comprising a tubular member through which said electron bunches pass, and means for applying to said tubular member a modulating potential having a high frequency potential less than said one frequency whereby said bunches of electrons in each cycle become compressed into groups of closely spaced bunches within said tubular member, and means within said tubular member for decelerating each bunch of electrons and a cavity resonator through which said groups of closely spaced bunches are directed to excite said resonator at a frequency substantially greater than said one frequency. a

14. The method of generating ultra high frequency oscillations which includes the steps of generating an electron beam, modulating said beam at one frequency to obtain equally spaced bunches of electrons, subjecting a plurality of successive bunches of electrons to successively increasing accelerating forces, passing said differentially accelerated bunches of electrons through a shielded space to cause said bunches to form a group of closely spaced bunches, and extracting energy from said grouped bunches of electrons at a frequency higher than said one frequency.

15. A method of generating ultra high frequency oscillations which includes the steps of generating an electron stream, modulating said stream at one frequency to obtain equally spaced bunches of electrons, periodically subjecting successive bunches to increasingly greater accelerating forces during each period, passing said differentially accelerated bunches of electrons through; a; shielded. space to cause" said bunches:

beam at; one frequency to obtain equally spaced.- bunches; ofelectrons, subjecting a plurality ofsuccessive bunches to l increasingly greater acceleratmg;forces, .whereby the: last bunch: of each cycle is given the greatest velocity, passing-1 said. difierentiallyaccelerated bunches of electrons througma shielded spacetocause-said bunches tmiorma group-of closely spaced. bunches, subjectingsaid; accelerated. bunches While in said. space to decelerating-forces to reduce the re-- quired' drift distance-for grouping, and extracting energy from said closely spaced bunches at a higherfrequency than saidv One-frequency.

135A, frequency changer according to claim 9, including a series of decelerating electrodes insulatedly mounted: along said path and within said tubular member betweensaid second: electrade: and said, partition, and means:- ior maintaininggsaid decelerating electrodes at.such-p0ten-- tials, that the same reverse field may be applied to all of said bunches todecelerate said bunchesas they pass through said drift tube.

18. A frequency changer. according to claim 5, further including. means in said shielded space for applying the same reverse electric field to all of said-bunches tozdecelerate said bunches as they pass through said space.

ERNEST G. LINDER.

REFERENCES CITED The. following references are of record in the file; of this patent:

UNITED STATES PATENTS Number Name Date.

2,222,899 Fraenckel NOV. 25, 19.4i0 2,222,901 Hahn Nov 26, 1940 2,401,945. Linder June 11, 1946 2,403,795 Hahn July 9, 1946 2,409,222. Morton Oct. 15, 1946 2,418,518 McArthur .Apr. 8, 1947 Certificate of Correction Patent N 0. 2,508,645 May 23,1950

ERNEST G. LINDER It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 5, line 51 strike out the Word substantiall column 6, line 29 a y strike out cathode and insert instead electrode; line 46, for potential read substantially and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Oifice. Signed and sealed this 30th day of January, A. D. 1951.

THOMAS F. MURPHY,

Assistant Commissioner of Pateats, 

